A pressure sensor is a device for measuring a pressure of a gas or a liquid, and is widely used for various applications such as industrial measurement, medical treatment, vehicle engine control, environmental control, and electronic appliance control.
The pressure sensor uses a displacement, a deformation, a magneto-thermal conductivity, or a frequency to measure the pressure. Recently, a micro pressure sensor manufactured by using a semiconductor technology has been popularized in terms of a small size, a low price, and a high performance.
The pressure sensors are mainly classified into a capacitive pressure sensor and a piezoresisive pressure sensor. The capacitive pressure sensor has a low temperature coefficient and low power consumption. However, capacitive pressure sensor requires a wide device area and a complicated signal processor since a capacitance is used as an output signal. The piezoresisive pressure sensor has an excellent linearity and easiness of signal processing. However, the piezoresisive pressure sensor has a low sensitivity and a large dependency on temperature. Therefore, the capacitive pressure sensor and the piezoresisive pressure sensor are selectively used according to characteristics of applications.
In the piezoresisive pressure sensor, a membrane having a closed structure is deformed by an external force, so that stress of a resistive material such as polysilicon or a piezoelectric transducer (PLT) formed on the membrane leads to a change in resistance. The pressure is measured from the change in resistance.
A conventional piezoresisive pressure sensor is manufactured by using a bulk (silicon) micromachining method and a hetero-substrate attaching method. More specifically, the piezoresisive pressure sensor is manufactured by attaching a first substrate having a membrane through the bulk micromachining for the substrates and a second substrate having a closed cavity formed on an upper or lower portion of the membrane. Typically, the first substrate is made of a silicon material, and the second substrate is made of a pyrex glass material.